Fig. 6

Layer 1 in the ACC of the adult non-human primate (rhesus macaque). a Section labeled with Nissl showed a moderate density of neurons and glia, mainly astrocytes, in layer 1 (examples of neurons are marked with orange arrows, glial cells are marked with green arrows). Superficially, the glia limitans was visible as a dense band of astrocytes (shown with black arrows). b Myelin (Gallyas) stain showed the relatively light band of myelinated axons within superficial layer 1 in ACC. This band was lighter than that seen in LPFC, following overall trends in myelination between those areas. Black arrows show axons entering layer 1 from layer 2. c Toluidine blue labeling of a 1 μm thick section from osmicated tissue revealed Nissl-stained cells and their processes, including profiles of myelinated axons (shown with black arrows in inset). There was a low density of axon profiles in superficial layer 1, in line with the light myelin stain shown in (b). Scale bar in inset measures 10 μm. d α-CamKII is a marker of synaptic plasticity. It labeled a dense population of processes in layer 1. e NeuN labeled all layer 1 neurons that were labeled with Nissl (not shown). NeuN labeling clearly showed that the density of labeled neurons in layer 1 was low, and the majority of the cellular density in layer 1, as seen in (a), was not due to neurons but instead could be attributed to glia. f-g GABA (f) and GAD67 (g) labeled inhibitory neurons in the cortex (labeled with black arrows). There was a moderate density of labeling in both sections, comparable to what was seen in the NeuN stain (c). h-j CB, CR, and PV labeled subpopulations of inhibitory interneurons. CB (h) and PV (j) labeled primarily neuron processes in layer 1 in the adult non-human primate, while CR (i) labeled few cell bodies (shown with black arrows). Black arrows in (j) show PV-labeled axons. k Microglia with various morphologies, labeled with Iba-1, could be seen in layer 1. l GFAP labeled the cell bodies and dense processes of astrocytes within layer 1 (shown with green arrows). Images were acquired such that the top edge of the images underlie the pia. Dotted lines indicate the border with layer 2 in all panels. Calibration bar in (l) applies to all panels